Heat-developable photographic light-sensitive materials and methods for forming images using the materials are well known and are described in detail, for example, in Shashin Kogaku no Kiso (Fundamentals of Photographic Engineering), Corona Co., Ltd., pp. 553 to 555 (1979), Eizo Joho (Image Information) (April, 1978), pp. 40, and Neblett's Handbook of Photography and Reprography, 7th Ed., Van Nostrand Reinhold Company, pp. 32 to 33 (1977), etc.
Typical examples of organic silver compounds which can be used in heat-developable light-sensitive materials include silver salts of aliphatic carboxylic acids and silver salts of aromatic carboxylic acids.
Further examples include silver salts of aliphtic carboxylic acids having a thioether group as described in U.S. Pat. No. 3,330,663.
However, these silver salts of carboxylic acids are disadvantageous in that they release acids after reacting with reducing agents to reduce the pH in the layer and thus subsequent development is restrained.
Organic silver salts other than silver salts of carboxylic acids include silver salts of compounds having a mercapto group, or a thione group, and derivatives thereof.
Additional examples include silver salts of compounds having an imino group such as silver salts of benzotriazole or derivatives thereof, etc., as described in Japanese Patent Publication Nos. 30270/69 and 18416/70.
However, these silver salts are disadvantageous in that they release a compound which restrains development, or, in some cases, causes fog after reacting with reducing agents. Furthermore, they sometimes inhibit the functions of spectral sensitizing dyes, and high sensitivity cannot be obtained.
Moreover, into heat-developable light-sensitive materials, bases or base precursors are frequently incorporated for the purpose of accelerating development by heat. In view of preservability of the light-sensitive materials, it is particularly preferred to employ base precursors which release basic substances upon thermal decomposition. In such cases, as the amount of the base precursor incorporated into the light-sensitive material is increased, development is accelerated. It is, however, accompanied with undesirable side-effects such as an increase of fog and inhibition of the functions of spectral sensitizing dyes, etc. Therefore, it is desired to employ the base precursor in an amount as small as possible.
In such circumstances, it has been desired to provide a highly active organic silver compound which can form images having high density even when only a small amount of a base precursor is employed.